Photocell controlled circuit

ABSTRACT

A photocell controlled circuit having an electrically conductive supporting plate or frame, including a first electrical contact portion affixed thereto and adaptable for connection to an electric load such as a lamp. A heat-responsive plate-like metallic element is carried by the supporting plate and electrically insulated therefrom and includes a temperatureresponsive, movable cutaway blade portion which carries a second electrical contact. The temperature of the bimetallic element is controlled by means of a heating resistor. This heating resistor comprises a resistive coating on a ceramic substrate. This resistor is operable to change the temperature of the ceramic substrate which is placed in movable electric contact with the blade portion of the bimetallic element. The amount of heat deliverable by the substrate may be controlled in relation to the position of the movable blade portion of the bimetallic element. The photocell is insulatively mounted on the supporting plate with one terminal of the photocell in electrical contact with another portion of the heating resistor. The other terminal of the photocell is adopted for connection to ground.

United States Patent [191 Schacht et al.

[ 1 Oct. 21, 1975 PHOTOCELL CONTROLLED CIRCUIT [76] Inventors: Ezra L. Schacht; Daniel Jay Schacht, both of 1620 W. Main St., Houston, Tex. 77006 [22] Filed: June 27, I974 [21] Appl. No.: 483,032

[52] US. Cl. 250/206; 315/159; 317/124;

337/103; 337/107 [51] Int. Cl. H0111 47/24; l-l0ll-l 61/013 [58] Field of Search 250/206, 239; 315/149,

Primary Examiner-Harold A. Dixon Assistant ExaminerE. R. LaRoche [57] ABSTRACT A photocell controlled circuit having an electrically conductive supporting plate or frame, including a first electrical contact portion affixed thereto and adaptable for connection to an electric load such as a lamp. A heat-responsive plate-like metallic element is carried by the supporting plate and electrically insulated therefrom and includes a temperature-responsive, movable cutaway blade portion which carries a second electrical contact. The temperature of the bimetallic element is controlled by means of a heating resistor. This heating resistor comprises a resistive coating on a ceramic substrate. This resistor is operable to change the temperature of the ceramic substrate which is placed in movable electric contact with the blade portion of the bimetallic element. The amount of heat deliverable by the substrate may be controlled in relation to the position of the movable blade portion of the bimetallic element. The photocell is insulatively mounted on the supporting plate with one terminal of the photocell in electrical contact with another portion of the heating resistor. The other terminal of the photocell is adopted for connection to ground.

22 Claims, 9 Drawing Figures US. Patent Oct. 21, 1975 Sheet10f2 3,914,598

PHOTOCELL CONTROLLED CIRCUIT BACKGROUND OF THE INVENTION The present invention relates generally to a photocell controlled circuit. More particularly, the invention relates to an improved photocell controlled heat responsive switch which provides greater reliability and predictability of performance as a result of improved thermal control.

Conventionally, load circuits such as lighting circuits of the type utilized to flood streets, buildings, parking lots, and the like with light at night, frequently employ devices to energize the lighting circuit in response to the intensity of available solar light. For example, such devices might be utilized to automatically energize lighting circuits at dusk and deactivate the lighting circuits at dawn. These switching devices of the prior art may employ a timing mechanism which is activated in response to a preselected intensity of available solar light. The timing mechanism determines the duration of energization of the light circuit, and another light responsive circuit operates to reset the device. In this manner, a lighting system may be automatically energized after sunset, remain energized for a predetermined length of time, and then automatically reset itself for another cycle triggered by the following sunset. An example of such a device is disclosed in U.S. Pat. No. 3,789,220, to Ezra L. Schacht.

Many light responsive or photocell controlled electric circuits and switches of the prior art are responsive to the detection of an intensity of light falling within a known range. This range has been found to vary widely, with the result that a group of lighting circuits independently energized by photocell controlled switches, when exposed to the same intensity of light, might respond to the light at different times over a period approaching an hour. In certain applications, for example street lamps, a random energization of light circuits over such a long period of time might be highly undesirable. In the case of street lamps, there might be a distraction to drivers of vehicles or other safety problems associated with the random energization of the lamps. In addition, in situations where the intensity of the light detected by the photocell does not range widely between an energization level and a deenergization level, it is possible, and indeed likely, that prior art devices may fail to provide a necessary predictability and reliability to perform satisfactorily.

There are known electric circuits wherein a heatactuated mechanism functions to displace the contacts of a switch. These heat-actuated mechanisms may be made responsive to heating elements the temperature of which are controlled in relation to the intensity of light detected by a photocell. It has been found that very few prior art devices utilizing'such heat-actuated switching mechanisms provide the predictability and reliability required for narrow range light intensity applications. Moreover, a variety of problems may be associated with the generation of a uniform gradient of heat in those heating elements.

It would, therefore, be highly desirable to provide a novel apparatus which remedies these and related problems which remain in the prior art.

OBJECTS AND SUMMARY OF A PREFERRED EMBODIMENT OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a novel photocell controlled circuit which substantially eliminates problems in the prior art of the type previously noted.

It is a more particular object of the present invention to provide a novel photocell controlled electric switch having a threshold light intensity which is predictable within a relatively narrow range of values.

It is another object of the present invention to provide a novel photocell controlled heat-actuated electric switch which incorporates a heating element which is used to trigger the switch with improved predictability and reliability than devices of the prior art.

It is a further object of the present invention to provide a novel photocell controlled electric switch which is simple in nature, reliable in use, and low in cost.

A preferred embodiment of the present invention comprises a photocell controlled electric switch having an electrically conductive supporting plate or base including a first electrical contact portion adapted for connection to a load. A heat-responsive plate-like bimetallic element is carried by the supporting plate and is electrically insulated therefrom. This bimetallic element includes a temperature responsive, movable cutaway blade portion and a second electrical contact carried by the blade portion and adaptable for connection to a power supply. A resistor defining a heating element and comprising a resistive coating on an electrically non-conductive substrate is mounted on the bimetallic element and is movable with the blade portion thereof. One edge of the resistive coating is placed in electrical contact with the bimetallic element. A photocell is insulatively mounted on the supporting plate and one terminal thereof is electrically connected to the other edge of the resistive coating. The other terminal of the photocell is adapted for connection to ground.

The heating element may be provided with a means responsive to a displacement of the movable blade portion for reducing the heat produced by the heating element to a minimum level satisfactory to maintain the bimetallic element in its displaced condition.

Other objects, advantages, and features of the present invention will become readily apparent to those skilled in the art upon consideration of the following detailed description and with reference to the following drawings, wherein like elements have been identified with like numerals, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially sectioned pictorial view of a photocell controlled single-pole single-throw electric switch accordingrto the present invention;

FIG. 2 is an exploded view of the apparatus illustrated in FIG. 1;

FIG. 3 is a plan view of an alternative embodiment of a thermal substrate of the present invention;

FIG. 4 is a plan view of another alternative embodiment of a thermal substrate of the present invention;

FIG. 5A is a side view of a photocell controlled single-pole single-throw electric switch in a contact-closed mode and wherein the thermal substrate of FIG. 4 is utilized;

FIG. 5B is the apparatus shown in FIG. 5A but in a contact-open mode;

FIG. 6 is a pictorial view of a bimetallic element having dual contacts to provide a double-pole single-throw electric switch according to the present invention;

FIG. 7 is a schematic diagram illustrating the basic electrical circuitry embodying the apparatus of FIGS. 1 and 2; and

FIG. 8 is a schematic diagram illustrating the basic electrical circuitry embodying the apparatus of FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION With reference now to FIGS. 1 and 2 there may be seen an apparatus 10 of the present invention. A metallic frame or plate 12 is utilized as a base portion of the apparatus 10. This frame 12 has an enlarged portion 14, a transverse portion 16, and a smaller portion 18. The enlarged portion 14 has a pair of apertures 20 and 22 of a size appropriate to receive a pair of insulating shoulder washers 24 and 26. A reduced diameter portion 28 and 30 of these insulating shoulder washers 24 and 26 respectively pass through the apertures. An enlarged diameter portion 32 and 34 of the shoulder washers 24 and 26 respectively may rest on a bottom surface 36 of the enlarged portion 14.

A photocell 38 is housed in a disc shaped housing 40 through which pass a pair of leads 42 and 44. This photoelectric cell, which is known in the art and specifically in which no invention is claimed alone, may have a resistance of 1,000 Ohms in light equivalent to full day light which resistance may increase to l Megohm in full darkness. In appropriate circumstances, a light shield (not shown) may be utilized to minimize the affeet on the photocell of artificial light sources, including those light sources controlled in accordance with this invention.

The leads 42 and 44 pass through small central bores 46 and 48 in the shoulder washers 24 and 26 respectively to thereby insulate these leads 42 and 44 from the frame 12. Whereas the photocell 38 is electrically insulated from the frame, the disc shaped housing 40 abuts against a top surface 50 of the enlarged portion 14 of the frame 12. The frame 12 is operable, therefore, as a heat sink for the photocell 38 and its housing 40. The enlarged portion 14 of theframe 12 may be yet further enlarged or fashioned from a higher gauge metal to yet further facilitate its heat absorbing capacity. Whereas a variety of metals may be utilized in the fabrication of the frame of base 12, it has been found that copper provides particularly advantageous characteristics both as an electrical conductor and as a heat sink in accordance with the present invention.

One lead 42 of the photocell 38 is passed through the shoulder washer 24 and electrically and mechanically connected, e.g., soldered, to a thermal substrate contact spring 52. This contact spring 52 has a shortened portion 54, a transverse portion 56, and an elon gate portion 58. The shortened portion 54 has a small aperture 60 to receive the lead 42 of the photocell 38.

With the shorter portion 54 of the contact spring 52 attached to the lead 42 of the photocell, the transverse bmbh's's and the longer portion 58 become operable as a spring arm. The longer portion 58 has a rectangular aperture 62 which, as will be more fully explained below, is cooperable with a square-shanked, flagged eyelet 64 to provide a movable electrical contact between the photocell lead 42 and a thermal substrate 68.

Referring now to the other photocell lead 44, it may be seen in FIGS. 1 and 2 that an eyelet 70 is electrically and mechanically attached, e.g., soldered, to the lead A heat-responsive bimetallic-element 72, which may be fashioned in accordance with the principles disclosed in the Taylor U.S. Pat. No. 2,503,008, is insulatively attached to the smaller portion 18 of the base 12 by means of a nut 74 and a bolt 76, the shank 78 of which passes through an aperture 80 in the smaller portion 18. A pair of insulating washers 82 and 84 are used in this attachment. An eyelet 86 is provided to facilitate making an electrical connection to a contact of the switch. This bimetallic blade assembly 72 is operable to provide a snap-action for opening and closing the switched contacts 88 and 90 of the circuit. The bimetallic blade is cutaway in such a manner as to define a movable blade 92 to which one of the contact elements 88 may be affixed in any conventional manner. The bimetallic element 72 is provided with a stamped out fastening portion 94 provided with an aperture 96 through which may be received the fastening bolt 74 to affix the bimetallic element 72 relative to the base or frame 12.

As a result of the displacement of the stamped portion 94, a pair or outboard strips 98 and 100 of the bimetallic element are stressed towards one another. This stressing will cause the bimetallic element to deform in its length and across its breadth, and since the movable center leg or blade 92 of the element is free, the blade 92 will tend to deflect to one side or the other of its original plane while also buckling about its center line.

Whereas a variety of bimetallic combinations may be suitable in the fabrication of the apparatus of the present invention, it has been found that the combination of brass and invar may be particularly suitable.

When the bimetallic element 72 is insulatively affixed to the frame 12, the contact 88 on the center blade 92 of the bimetallic element is movable between a position of engagement with a contact portion 96 of the frame 12 and a position of nonengagement, depending upon the temperature of the bimetallic element. It is this pair of contacts 88 and 90 which function to energize or deenergize the electric load shown in FIG. 7.

The temperature of the bimetallic strip is controlled by the thermal substrate 68. This thermal substrate is operable as a heater to selectively raise the temperature of the bimetallic element 72 to a threshold level whereupon the central blade 92 will snap to a displaced position which will disengage the contacts 88 and 90. This snap-action occurs as a result of the prestressing of the bimetallic element and advantageously minimized undesirable arcing. It will, of course, be appreciated that the element 72 may be mounted on the frame 12 in a manner to provide an engagement of the contacts 88 and 90 upon the heating of the element.

This heater device 68 is comprised of a ceramic substrate 102 coated with thick-film resistive material 104 which has conductive tabs 106 and 108 attached at two edges thereof. The square shanked flagged eyelet 64 referred to above is attached, e.g., soldered, to the conductive tab 108. A substrate-to-bimetallic-element contact spring 110 is, appropriately attached, e.g. soldered, to the other conductive tab' 106. It is through this contact spring 110 that the bimetallic element 72 is placed in electrical contact with the thick-film resistive material 104 on the ceramic substrate 102. The

contact spring 110 and the bimetallic element 72 are in sliding engagement, and electrical contact may be achieved so long as any portion of the contact spring 110 engages the bimetallic element 72.

The square shanked flagged eyelet 64 has a square or frusto-pyramidical shank portion 1 14 which cooperates with the rectangular aperture 62 in the elongate portion 58 of the photocell-to-thermal-substrate contact spring 52. With this arrangement, the thermal substrate 68 may float between the bimetallic element 72 and the contact spring 52. In this manner, the thermal substrate 68 may remain in physical contact with the center leg or blade 92 of the bimetallic element 72 when the blade 92 is in an open-contact mode and without imposingundesirable forces on the bimetallic element 72 which would interfere with the operation thereof. Hence, there is provided a relatively easily assembled thermal substrate having a ceramic base which remains in physical contact with the blade of the bimetallic element at all times during heated operation of the bimetallic element and without imposing undesirable stresses or forces on the element.

There may be seen in FIGS. 3 and 4 drawings of alternative thermal substrates which may be used in connection with the present invention. With reference to FIG. 3, there may be seen a thermal substrate 116 having first length of electrically conductive material 118 etched, screen printed and fired or otherwise appropriately attached to a ceramic substrate 120. A pair of thick-film resistive strips 122 and 124 have their respective ends 123 and 125 electrically connected, e.g., soldered, to this conductor portion 118. A T-shaped conductor portion 126 is attached to the substrate 120 and makes electrical contact with the other ends 128 and 130 of the resistive strips 122 and 124 respectively. This T-shaped conductor 126 is connected to an enlarged rectangular pad 132. A square shanked eyelet (see FIGS. 5A and 5B) is electrically attached to this pad 132. By separating the resistive strips or heaters 122 and 124, this arrangement is operable to divide the heat generating portion of the thermal substrate 116 into two zones to provide an advantageous distribution of heat across the sufaces of the ceramic material 120. In addition, the arrangement of the elements of the alternative embodiment shown in FIG. 3 may significantly facilitate assembly of the thermal substrate 116.

Another alternative embodiment of the thermal substrate is shown in FIG. 4. This embodiment is substantially similar to that shown in FIG. 3 but with several important differences. It will be appreciated that although the substrates shown in FIGS. 3 and 4 appear to differ structurally only slightly, these substrates function to achieve significantly different results.

In the substrate shown in FIG. 4, a length of conductive material 138 is divided into two portions. A gap separates the conductive material 138 at an off-center location. A first conductor portion 140 is approximately half the length of a second conductor portion 142. The first portion 140 is electrically attached to an end 141 of a first length 144 of a thick-film resistive material. The second portion 142 is electrically attached to an end 143 of another length 146 of a thickfilm resistive material. As in the case of the thermal substrate 116 illustrated in FIG. 3, a T-shaped conductor portion 148 is attached to the other ends 150 and 152 of the resistive strips 144 and 146 respectively. This T-shaped conductor 148 is connected to an enlarged rectangular pad 154 to which may be attached the square shanked eyelet 134 (see FIGS. 5A and 5B).

The substrate-to-bimetallic element contact spring 155 is also divided into two parts 156 and 158 which correspond lengthwise to the two conductors 140 and 142 respectively. The resistive strips 144 and 146 are placed in parallel when the two contact springs 156 and 158 are both seated against corresponding contact areas 160 and 162 of the bimetallic element 72 (see FIG. 2), which condition would exist in the apparatus shown when the blade 92 is displaced towards the frame 12 in a contact-closed mode.

As may be seen in FIGS. 5A and 5B, when the bimetallic blade 92 snaps to a contact-open mode as a result of being heated to a threshold temperature by the thermal substrate, the blade 92 will displace the substrate 136 to an extent that the contacts made at the contact zones 162 and 160 with the springs 156 and 158 respectively are broken. However, a contact zone 164 on the blade 92 engages the longer spring 158 portion to remake" the electrical contact between the spring 158 and the bimetallic element.

As a result of the arrangement of elements in connection with the embodiment shown in FIG. 4, only one of the resistive strips is now in the circuit. Resistive strip 146 remains in the circuit, the other resistive strip 144 having been open-circuited because the smaller spring 156 is no longer in electrical contact with any portion of the bimetallic element. There results an advantageous variable resistance across the surface of the thermal substrate. With this arrangement, once the switch has been openedas a result of heating the thermal substrate to the threshold temperature of the bimetallic blade, the power in the circuit may be reduced to permit the thermal substrate to achieve a temperature closer to the threshold temperature of the bimetallic element 72. With this arrangement, the difference between the switch-open and switch-closed ambient light levels may be reduced as will be hereinafter more fully explained.

With both resistive strips 144 and 146 engaged in the circuit, when it is-desired to raise the temperature of the thermal substrate, the temperature of thermal substrate 136 may be raised relatively quickly to a level in excess of the threshold temperature of the bimetallic element 72. Once the threshold temperature is achieved and the contacts 88 and 90 open, one of the resistive elements is removed from the circuit, and a reduced amount of heating power is delivered to the thermal substrate 136. As a result of the reduced power delivered to the thermal substrate, the temperature of the bimetallic element 72 is reduced to a value lying closer to the threshold temperature of the bimetallic element than if both the resistive elements 144 and 146 remained in the circuit.

Hence, with the alternative embodiment illustrated in FIG. 4, the apparatus relatively quickly heats the thermal substrate 136 to the threshold temperature of the bimetallic element 72 and then reduces the power delivered to the substrate in order to'reduce the temperature of the bimetallic element to a point lying only slightly above the threshold temperature. This provides a circuit responsive to relatively slight differences in light intensity delivered to the photocell 38.

Another embodiment of the present invention may utilize a bimetallic element 166 as illustrated in FIG. 6. This embodiment provides a double-pole single-throw electrical switch operable in principle in much the same manner as the apparatus described in connection with FIGS. 1 and 2. This embodiment differs essentially in that a blade portion 168 of the bimetallic element 166 is anchored to a frame 167'byrrieans of a bolt (not shown) through apertures 170 and 171. An insulated strip 172 is carried by a transverse portion 174 ofthe bimetallic element 166. A pair of contacts 176 and 178 are carried by this insulated strip. A pair of corresponding contacts 175 and 179 may be insulatively carried by an insulator 181 mounted on the frame 167 in order to provide double-pole singlethrow operation. Other aspects of an embodiment utilizing the arrangement illustrated' in FIG. 6 will correspond to those described in connection with FIGS. 1 and 2 and will not be repeated.

FIG. 7 is a schematic representation of a photocell controlled circuit 173 which utilizes a thermal substrate depicted in FIG. 4 in accordance with the present invention-This photocell controlled circuit triggers a switching circuit 177 operable in response to a reduction in intensity of light sensed by the photocell 38 to' energize an electric load 178, for example, a lamp.

The photocell 38 operates in a manner to increase a resistance seen across its terminals 42 and 44 in response to a decrease in incident ambient light imposed on the'photocell 38. It will be appreciated, therefore, that the photocell is operable to control the amount of current flowing across a pair of resistors 180 and 182 as shown in FIG. 7. These resistors might, for example, correspond to resistance strips 144 and 146 respectively of the thermal substrate 136.

A source of voltage, which may be from conventional power lines, e.g., 120 volts AC, is introduced at a pair of terminals 184 and 186. When relatively high intensity light is imposed on the photocell 38, the resistance across the photocell drops witha resulting greater current flow in the resistors 180 and 182. Current flow through normally close contacts 192 and 194 and the resistors 180 and 182 produces heat in excess of a threshold temperature of the bimetallic element. This causes the blade to displace to a position to separate the contacts 188 and 190. The contacts 192 and 194 also open to remove one of the resistors 182 from the heating circuit. It will, of course, be appreciated that the heat produced by this resistor 180 is alone sufficient to maintain the heat-responsive switch above the threshold temperature in a contact-open mode.

The contacts 188 and 190 might, for example, correspond to the contacts 88 and 90, and the contacts 192 and 194 might, for example, correspond to the contacts 162 and 156. The terminals 184 and 186 might, for example, correspond to eyelets 86 and 70 respectively. The conductor 200 of the circuit might, for example, correspond to the frame or plate 12. the plate 12 may carry an eyelet 13 which would correspond to a terminal 202 shown in FIG. 7.

Upon a reduction of the incident light on the phtocell 38, the resistance across the terminals 42 and 44 of the photocell increases with a result that current flow to the resistor 180 is reduced. This reduction in current flow in the resistor provides less heating energy to the resistor, and the thermal substrate is able to cool to a temperature below the threshold temperature of the bimetallic element. The bimetallic blade displaces the blepole single-throw switching arrangement 196 described in connection with FIG.-6.

The photocell controlled circuit 173 shown in FIG. 8 corresponds essentially to the apparatus shown in FIGS. 1 and 2. A heating element or resistor 198 might, for example, correspond to the resistive strip 104 shown in FIG. 1. The double-pole single-throw switch might, for example correspond to the apparatus shown in FIG. 6.

SUMMARY OF ADVANTAGES AND SCOPE OF THE INVENTION Thus, it may be seen, that in the practice of the present invention certain distinct advantages may be realized. Forexample, the thermal substrate of the present invention provides a more uniform heat transfer to actuate the bimetallic element of the circuit. In addition, because the thermal substrate slippingly engages the bimetallic element, undesirable stresses imposed on the bimetallic switch by the heating element are minimized.

Of independent significance is an advantageous reduction in the heat generating capacity of ,the thermal substrate in response to the threshold temperature displacement of the blade of the bimetallic element. This arrangement facilitates advantageous control and predictability in a circuit controlled by the apparatus of the present invention.

In addition, the photocell is protected. from undesirable and destructive over-heating as a result of its advantageous positioning on the frame portion of the present invention. This frame is operable as arr-electrical conductor for a portion of the circuit and, as a heat sink for the photocell.

It, therefore, may be seen that the present invention is well adapted to attain substantially all of the objects and advantages hereinabove setforth together with other advantages which will become apparent from the description of the apparatus. This description, including the alternative embodiments, are intended as illustrative of the concept of the present invention, and it is intended that other embodiments be considered as falling within the spirit and scope of the present invention.

What is claimed is:

l. A light responsive, photocell controlled electrical switch comprising:

a supporting frame;

first electrical contact means carried by said frame, said first contact means adaptable for connection to a load;

a metallic heat-responsive element insulatively carried by said frame, said element having a temperature-movable portion;

second electrical contact means carried by said temperature-movable portion of said element, said second contact means adaptable for connection to a power source;

heating means fof controlling the temperature of said temperature-movable portion of said element, said heating means comprising: an electrical!y-nonconductive substrate, said substrate having a top surface and a bottom surface, said substrate being movable with said temperature-movable portion;

a resistive coating carried by said top surface of said substrate; I

a bottom terminal on said bottom surface of said substrate-in electrical communication with said resistive coating, said bottom terminal being operable to maintain slidable electrical and mechanical contact with said heat-responsive element;

a top terminal on said top surface of said substrate in electrical communication with saidresistive coating; and I photocell means insulatively mounted on said frame having one terminal electrically connected to said top terminal for controlling an amount of electric current delivered to said resistive coating from the power source, the other terminal of said photocell means being adaptable for connection to ground.

2. The apparatus of claim 1 wherein said heatresponsive element comprises a plate-like bimetallic element.

3. The apparatus of claim 2 wherein said temperature-movable portion of said heat-responsive element comprises a cutaway blade portion of said plate-like bimetallic element.

4. The apparatus of claim 1 whereinsaid heatresponsive element comprises a plate-like bimetallic element having a cutaway blade portion and a transverse portion, and wherein said temperature-movable portion of said heat-responsive element comprises said transverse portion.

5. The apparatus of claim 4 wherein said first electrical contact means comprises a pair of contacts insulatively carried by said frame.

6. The apparatus of claim 5 wherein said second electrical contact means comprises a pair of contacts insulatively carried by said transverse portion of said heatresponsive element.

7. The apparatus of claim 1 wherein said heating means comprises a second resistive coating carried by said substrate, a second bottom terminal on said bottom surface of said substrate in electrical communication with said second resistive coating, said second bottom terminal being operable to maintain slidable electrical and mechanical contact with said heat-responsive element; said top terminal on said top surface of said substrate being in electrical communication with said second resistive coating.

8. The apparatus of claim 7 and further comprising means for open-circuiting said second resistive coating in responsive to a movement of said temperaturemovable portion of said heat-responsive element.

9. The apparatus of claim 8 wherein said apparatus is operable to actuate said first and second electrical contact means and said open-circuiting means substantially simultaneously in response to the movement of said temperaturemovable portion of said heatresponsive element. I

10. A light responsive, photocell controlled electrical lamp comprising:

an electrical lamp circuit; a power input means for delivering power to energize said electrical lamp circuit;

switch means responsive to a preselected intensity of ambient light for selectively placing said electrical lamp circuit and said power input means in electrical communication, said switch means comprising: a supporting frame;

a heat-responsive element insulatively carried by said frame, said element having a temperaturemovable portion operable to selectively place said lamp circuit and said power input means in electrical communication in response to a position of said temperature-movable portion; heating means for controlling the position of said temperature-movable portion of said element, said heating means comprising:

an electrically-nonconductive substrate having a top surface and a bottom surface, said substrate being movable with said temperature-movable portion;

a resistive coating carried by said substrate;

a bottom terminal on said bottom surface of said substrate in electrical communication with said resistive coating, said bottom terminal being operable to maintain slidable electrical and mechanical contact with said heat-responsive element;

a top terminal on said top surface of said substrate in electrical communication with said resistive coating; and' photocell-means insulatively mounted on said frame having one terminal electrically connected to said top terminal for controlling an amount of electric current delivered to said resistive coating from the power source, the other terminal of said photocell means being adaptable for connection to ground;

said switch means and said power input means being cooperable to provide power to said electrical lamp circuit when the intensity of the ambient light incident upon said photocell means falls below the preselected level.

ll. The apparatus of claim 10 wherein said heatresponsive element comprises a plate-like bimetallic element.

12. The apparatus of claim 1 1 wherein said temperature-movable portion of said heat-responsive element comprises a cutaway blade portion of said plate-like bimetallic element.

'13. The apparatus of claim 10 wherein said heatresponsive element comprises a plate-like bimetallic element having a cutaway blade portion and a transverse portion, and wherein said temperature-movable portion of said heat-responsive element comprises said transverse portion.

14. The apparatus of claim 13 wherein said first elec trical contact means comprises a pair of contacts insulatively carried by said frame.

15. The apparatus of claim 14 wherein said second electrical contact means comprises a pair of contacts insulatively carried by said transverse portion of said heat-responsive element.

16. The apparatus of claim 10 wherein said heating means comprises a second resistive coating carried by said substrate, a second bottom terminal on said bottom surface of said substrate in electrical communication with said second resistive coating, said bottom terminal being operable to maintain slidable electrical and mechanical contact with said heat-responsive element, and a top terminal on said top surface of said substrate in electrical communication with said second resistive coating.

17. The apparatus of claim 16 and further comprising means for open-circuiting said second resistive coating in response to a movement of said temperaturemovable portion of said heat-responsive element.

18. The apparatus of claim 17 wherein said apparatus is operable to actuate said first and said second electrical contact means and said open-circuiting means substantially simultaneously in response to the movement of said temperature-movable portion of said heatresponsive element.

19. The apparatus of claim wherein said edge of said resistive coating is electrically connected to a first spring, said first spring being operable to slidingly engage said heat-responsive element to provide a movable electrical contact between said heat-responsive element and said edge of said resistive coating.

20. A light responsive electrical contact actuating apparatus, comprising: p v, v

a supporting plate, carrying a first electrical contact portion adapted for connection to aload;

a heat-responsive ,plate-like bimetallic element carried by the supporting plate and electrically insulated therefrom, said element including a temperature-movable cutaway blade portion and a second electrical contact electrically co -ope rable with said first electrical contact, said second electrical contact being carried by the blade portion and adaptable for connection to a power supply;

a resistor comprisingz v I,

anelectrically nonconductive substrate having a top surface and a bottom surface opposite said top surface, said substrate being positioned so that at least a portion of said substrate ovprlies said bimetallic element and being movable with said blade portion to remain in contact with at least a portion of said blade portion regardless of the position of said blade portion;

a r esistive coating carried by said top surface of "said substrate;

a first bottom terminal on said bottom surface of said substrate in electrical communication with said resistive coating on said top surface, said bottom terminal being operable to remain in slidable electrical and mechanical contact with said bimetallic element regardless of the position of said blade portion of said bimetallic element;

a spring electrically and mechanically engagable with said resistor top terminal for urging said resistor bottom surface against said bimetallic element; and

a photocell insulatively mounted on said supporting plate, a first photocell terminal of said photocell being electrically connected to said top terminal of said resistor, a second photocell terminal of said photocell being adapted for connection to ground.

21. The apparatus of claim 20 and including a second resistor comprising:

a second resistive coating carried by said top surface of saidnonconductive substrate; and a a second bottom terminal-on said bottom surface of said substrate and operable to remain in slidable electrical and mechanical contact with said bimetallic element when said blade portion is in a first position;

said blade portion being operable in a second position to displace said second bottom terminal to a position to break electrical and mechanical contact with said bimetallic element.

22. The apparatus of claim '20 wherein said load is an electric lamp. 

1. A light responsive, photocell controlled electrical switch comprising: a supporting frame; first electrical contact means carried by said frame, said first contact means adaptable for connection to a load; a metallic heat-responsive element insulatively carried by said frame, said element having a temperature-movable portion; second electrical contact means carried by said temperaturemovable portion of said element, said second contact means adaptable for connection to a power source; heating means for controlling the temperature of said temperature-movable portion of said element, said heating means comprising: an electrically-nonconductive substrate, said substrate having a top surface and a bottom surface, said substrate being movable with said temperature-movable portion; a resistive coating carried by said top surface of said substrate; a bottom terminal on said bottom surface of said substrate in electrical communication with said resistive coating, said bottom terminal being operable to maintain slidable electrical and mechanical contact with said heat-responsive element; a top terminal on said top surface of said substrate in electrical communication with said resistive coating; and photocell means insulatively mounted on said frame having one terminal electrically connected to said top terminal for controlling an amount of electric current delivered to said resistive coating from the power source, the other terminal of said photocell means being adaptable for connection to ground.
 2. The apparatus of claim 1 wherein said heatresponsive element comprises a plate-like bimetallic element.
 3. The apparatus of claim 2 wherein said temperature-movable portion of said heat-responsive element comprises a cutaway blade portion of said plate-like bimetallic element.
 4. The apparatus of claim 1 wherein said heatresponsive element comprises a plate-like bimetallic element having a cutaway blade portion and a transverse portion, and wherein said temperature-movable portion of said heat-responsive element comprises said transverse portion.
 5. The apparatus of claim 4 wherein said first electrical contact means comprises a pair of contacts insulatively carried by said frame.
 6. The apparatus of claim 5 wherein said second electrical contact means comprises a pair of contacts insulatively carried by said transverse portion of said heatresponsive element.
 7. The apparatus of claim 1 wherein said heating means comprises a second resistive coating carried by said substrate, a second bottom terminal on said bottom surface of said substrate in electrical communication with said second resistive coating, said second bottom terminal being operable to maintain slidable electrical and mechanical contact with said heat-responsive element; said top terminal on said top surface of said substrate being in electrical communication with said second resistive coating.
 8. The apparatus of claim 7 and further comprising means for open-circuiting said second resistive coating in responsive to a movement of said temperature-movable portion of said heat-responsive element.
 9. The apparatus of claim 8 wherein said apparatus is operable to actuate said first and second electrical contact means and said open-circuiting means substantially simultaneously in response to the movement of said temperaturemovable portion of said heat-responsive element.
 10. A light responsive, photocell controlled electrical lamp comprising: an electrical lamp circuit; power input means for delivering power to energize said electrical lamp circuit; switch means responsive to a preselected intensity of ambient light for selectively placing said electrical lamp circuit and said power input means in electrical communication, said switch means comprising: a supporting frame; a heat-responsive element insulatively carried by said frame, said element having a temperature-movable portion operable to sElectively place said lamp circuit and said power input means in electrical communication in response to a position of said temperature-movable portion; heating means for controlling the position of said temperature-movable portion of said element, said heating means comprising: an electrically-nonconductive substrate having a top surface and a bottom surface, said substrate being movable with said temperature-movable portion; a resistive coating carried by said substrate; a bottom terminal on said bottom surface of said substrate in electrical communication with said resistive coating, said bottom terminal being operable to maintain slidable electrical and mechanical contact with said heat-responsive element; a top terminal on said top surface of said substrate in electrical communication with said resistive coating; and photocell means insulatively mounted on said frame having one terminal electrically connected to said top terminal for controlling an amount of electric current delivered to said resistive coating from the power source, the other terminal of said photocell means being adaptable for connection to ground; said switch means and said power input means being cooperable to provide power to said electrical lamp circuit when the intensity of the ambient light incident upon said photocell means falls below the preselected level.
 11. The apparatus of claim 10 wherein said heat-responsive element comprises a plate-like bimetallic element.
 12. The apparatus of claim 11 wherein said temperature-movable portion of said heat-responsive element comprises a cutaway blade portion of said plate-like bimetallic element.
 13. The apparatus of claim 10 wherein said heat-responsive element comprises a plate-like bimetallic element having a cutaway blade portion and a transverse portion, and wherein said temperature-movable portion of said heat-responsive element comprises said transverse portion.
 14. The apparatus of claim 13 wherein said first electrical contact means comprises a pair of contacts insulatively carried by said frame.
 15. The apparatus of claim 14 wherein said second electrical contact means comprises a pair of contacts insulatively carried by said transverse portion of said heat-responsive element.
 16. The apparatus of claim 10 wherein said heating means comprises a second resistive coating carried by said substrate, a second bottom terminal on said bottom surface of said substrate in electrical communication with said second resistive coating, said bottom terminal being operable to maintain slidable electrical and mechanical contact with said heat-responsive element, and a top terminal on said top surface of said substrate in electrical communication with said second resistive coating.
 17. The apparatus of claim 16 and further comprising means for open-circuiting said second resistive coating in response to a movement of said temperature-movable portion of said heat-responsive element.
 18. The apparatus of claim 17 wherein said apparatus is operable to actuate said first and said second electrical contact means and said open-circuiting means substantially simultaneously in response to the movement of said temperature-movable portion of said heat-responsive element.
 19. The apparatus of claim 10 wherein said edge of said resistive coating is electrically connected to a first spring, said first spring being operable to slidingly engage said heat-responsive element to provide a movable electrical contact between said heat-responsive element and said edge of said resistive coating.
 20. A light responsive electrical contact actuating apparatus, comprising: a supporting plate, carrying a first electrical contact portion adapted for connection to a load; a heat-responsive plate-like bimetallic element carried by the supporting plate and electrically insulated therefrom, said element including a temperature-movable cutaway blade portion and a second electrical contact electricaLly co-operable with said first electrical contact, said second electrical contact being carried by the blade portion and adaptable for connection to a power supply; a resistor comprising: an electrically nonconductive substrate having a top surface and a bottom surface opposite said top surface, said substrate being positioned so that at least a portion of said substrate overlies said bimetallic element and being movable with said blade portion to remain in contact with at least a portion of said blade portion regardless of the position of said blade portion; a resistive coating carried by said top surface of said substrate; a first bottom terminal on said bottom surface of said substrate in electrical communication with said resistive coating on said top surface, said bottom terminal being operable to remain in slidable electrical and mechanical contact with said bimetallic element regardless of the position of said blade portion of said bimetallic element; a spring electrically and mechanically engagable with said resistor top terminal for urging said resistor bottom surface against said bimetallic element; and a photocell insulatively mounted on said supporting plate, a first photocell terminal of said photocell being electrically connected to said top terminal of said resistor, a second photocell terminal of said photocell being adapted for connection to ground.
 21. The apparatus of claim 20 and including a second resistor comprising: a second resistive coating carried by said top surface of said nonconductive substrate; and a second bottom terminal on said bottom surface of said substrate and operable to remain in slidable electrical and mechanical contact with said bimetallic element when said blade portion is in a first position; said blade portion being operable in a second position to displace said second bottom terminal to a position to break electrical and mechanical contact with said bimetallic element.
 22. The apparatus of claim 20 wherein said load is an electric lamp. 